With the development of technology, mobile phones, digital cameras, tablet PCs, notebook computers and other portable electronic devices become more and more popular. The portable electronic devices are intended for personal use, with certain privacy. The information stored in the portable device such as phonebook, photos, personal information, etc., are privately owned. If the electronic device is lost, these data may be accessed by other people, causing unnecessary loss. Even though there are several ways using password to protect the electronic device from being used by the other people, the password may be easily to be spread or cracked, which lowers the security. Moreover, the user needs to remember the password so as to use electronic devices. If the user forgets the password, troubles would be brought to the user. Hence, personal fingerprint identification is utilized to achieve the purpose of personal identification, for enhancing the data security.
In the prior art, capacitive fingerprint recognition system is a popular fingerprint recognition technique, which uses a touch layer to receive a finger touch from a user, and senses a capacitance variation of the touch layer to determine whether it is a finger ridge or a finger valley of a fingerprint of the user. To prevent the touch layer from being interfered by other circuitry, in the prior art, a shielding layer is usually laid under the touch layer in IC layout, forming a shielding effect to prevent interference from the circuitry under the shielding layer. However, a parasitic capacitance is formed between the touch layer and the shielding layer. A capacitance of the parasitic capacitance is usually larger than a capacitance of a touch capacitance caused by touch, which has an impact on the capacitance determining circuit or the capacitance fingerprint recognition system determining the touch capacitance, such that accuracy of the fingerprint recognition system degrades.